High power amplifiers, such as radio frequency (RF) and microwave amplifiers, are typically constructed using high power, high frequency transistors built around a biasing and signal input/output circuit board, the transistors being encapsulated into standard flange mount packaging.
In use, high power amplifiers generally dissipate a large proportion of their operating energy as heat and, in some cases, from about 40% to about 90% of the operating energy of the amplifier may be lost as generated heat.
A number of means for managing this generated heat have been proposed.
For example, flange mount packaging may be bolted directly to a housing of the amplifier for heat transfer purposes.
A heat sink, such as a finned heat sink, may be provided in order to transfer heat to the surrounding atmosphere. In some instances, the amplifier housing may be bonded to the heat sink.
A forced air cooling fan may be provided to assist in directing heat from the amplifier and, in some instances, a cooling fan may be provided in addition to a heat sink to improve the effectiveness of the heat sink.
While the provision of a heat sink and/or a fan may assist in dissipating heat generated by the amplifier, the heat sink and fan components add significantly to the volume occupied by the amplifier resulting in a relatively bulky device. For example, a heat sink will often comprise relatively large volumes of metal, such as aluminum or other conductor, and a large number of fins to dissipate the heat. Thus, when using a heat sink the relatively small transistor has to heat up a significant volume of material, such as metal, for a long period of time before thermal equilibrium is achieved, which is not efficient.
More recently, heat sinks developed for the microprocessor industry have evolved at a significant pace resulting in highly compact and efficient devices capable of removing high levels of heat from very compact footprints. For example, some microprocessor heat sinks utilise heat pipe technology which is highly efficient at removing heat using conduction and convection, or circulating fluid heat pipe technology. The heat pipes are located close to the surface of the heat sink which contacts the hot surface. Examples of heat pipe heat sinks may also use the latent heat of a fluid (for example, ethanol, acetone, water, sodium or mercury), solid high conductivity conductors or a circulated cooling fluid to extract the heat away from the hot surface to a heat exchanger or radiator which may or may not be fan assisted. Examples of known heat-pipe based microprocessor heat sinks include the Zalman VF2000 (RTM) VGA/CPU fan embedded solid heatpipe, TS Heatronics NCU-1000 (hydrofluorocarbon-134a liquid vapour heat pipe) and the Corsair H70 (pumped water heatsink with fan assisted heat exchanger).
Microprocessor heat sinks are specifically designed to couple directly onto the heatspreader of a modern microprocessor CPU. The heatspreader is the physical surface (typically the top) of the CPU encapsulating case. The CPU heatspreader is flat and may be polished to facilitate maximum heat transfer into the heatsink. A microprocessor heatsink usually has features that are compatible with the CPU socket (or CPU slot) which is the mechanical component that provides mechanical and electrical connection between the microprocessor and the computer motherboard. (an example of a CPU socket is the Intel LGA 775).
With any heat sink, in order to facilitate efficient transfer of heat from a transistor to the heat sink, it is desirable to minimize the number of thermal junctions between the transistor and the heat sink, since each junction acts as an insulating layer reducing the heat sink efficiency. Thus, it is desirable to locate the transistor directly onto the heat sink to provide a single thermal junction.
However, heat pipe and water flow based heat sinks by their design cannot accommodate this type of direct connection. In particular, one problem associated with these heat sinks is that there is limited bulk metal between the heat pipe and the device to accommodate mounting flange bolts required to fasten the transistor directly to the heat sink.
Furthermore, it is necessary to extract the heat from transistors that are used in high power amplifiers in a very precise fashion.
In addition, a transistor may require a good electrical ground contact to a mounting flange which may not be provided if the transistor is bonded using an electrically insulating thermal paste.